Some of mankind's most devastating inherited diseases appear to be declining, and a few have nearly disappeared, because more people are using genetic testing to decide whether to have children.

Births of babies with cystic fibrosis, Tay-Sachs and other less familiar disorders seem to have dropped since testing came into wider use, The Associated Press found from interviews with numerous geneticists and other experts and a review of the limited research available.

Many of these diseases are little known and few statistics are kept. But their effects - ranging from blood disorders to muscle decline - can be disabling and often fatal during childhood.

Now, more women are being tested as part of routine prenatal care, and many end pregnancies when diseases are found. One study in California found that prenatal screening reduced by half the number of babies born with the severest form of cystic fibrosis because many parents chose abortion.

More couples with no family history of inherited diseases are getting tested before starting families to see if they carry mutations that put a baby at risk. And a growing number are screening embryos and using only those without problem genes.

The cost of testing is falling, and the number of companies offering it is rising. A 2008 federal law banning gene-based discrimination by insurers and employers has eased fears.

Genetic testing pushes hot-button issues: abortion, embryo destruction and worries about eugenics - selective breeding to rid a population of unwanted traits. Yet it is touching a growing number of people:

- In suburban Cleveland, Beth and Thad Meese were stunned to learn during her second pregnancy that they carry genes that can cause cystic fibrosis. Tests show the baby won't have the disease, but they have decided against having a third child or to screen embryos if they do. "I feel like we got lucky" and should not tempt fate again, she said.

- In Boston, Harvard psychologist and author Steven Pinker and his wife, novelist Rebecca Goldstein, learned last year that they carry genes that cause a serious neurological disease, familial dysautonomia. Too old to have children, they shared the news with younger relatives, who are being tested to see if they, too, have the gene. "There's a tendency psychologically to think these are very rare and what are the chances that two people could both have rare genes," Pinker said. "Not only can it happen, but it happened to me."

- In the Canadian city of Vancouver, Jeff and Megan Carroll screened embryos to have two children free of the Huntington's disease gene Jeff has. "I felt very strongly that I didn't want to pass on this," he said. Huntington's "is done killing people in my family when I am gone."

Although genetic testing can raise moral dilemmas, at least one conservative religious group - Orthodox Jews - has found ethically acceptable ways to use it to lessen diseases that have plagued its populations.

"I am a Holocaust survivor. I was born in the middle of the second World War. I hope that I am not a suspect for practicing eugenics. We are trying to have healthy children," said Rabbi Josef Ekstein of New York, who founded a group that tests couples and discourages matches when both carry problem genes.